This section provides background information related to the present disclosure, which is not necessarily prior art.
Brushless motors are commonly used for a variety of industrial and consumer products, such as automotive related products, in particular blower motors for heating, ventilation, and air conditioning (HVAC) systems. Brushless motors have replaced conventional DC brush motors for a variety of reasons. One of the main reasons is to avoid and eliminate the common excitation of brush noise that is induced due to contact and sliding of the brushes and commutator slots. The use of a brushless motor eliminates the brush noise, which is usually tonal (slot passing frequency corresponding to the number of slots on the commutator), as well as high frequency ticking/grinding noise.
Typical brushless motors have an odd number of magnets (m) and an even number of slots (s) on a stator and rotor or vice versa. As a result, current brushless motors can generate major magnetic harmonics at orders corresponding to (m·s)/2, and minor sub-harmonics at multiples of m (e.g., if m=5 and n=10, major audible harmonics may be excited at (5·10)/2=25th order of the rotational speed of the motor.
A brushless motor that suppresses this dominant harmonic would therefore be desirable. The present disclosure advantageously provides for such a brushless motor, which has dominant harmonics at higher orders, which are masked (inaudible) by the blower.
Current brushless motors experience dominant (audible) orders/tones at certain rotational speeds, relatively low blower speeds when the air-rush noise that usually masks blower-induced noise is minimal. The most dominant/audible tone (order) occurs at (m·n)/2 order. With current brushless motors, the product of (m·n) is an even number, and the order occurs at an integer number. This order gets further amplified when coincident with HVAC system resonances. For example, for existing brushless motors where m=4 and n=6, the dominant order is (4·6)/2=12. For current motors where m=8 and n=6, the dominant order is (8·6)/2=24. For current brushless motors where m=5 and n=6, the dominant order is (5·6)/2=15. Such dominant orders are undesirably audible because they are not masked by the air-rush noise of the blower due to the relatively low frequency and high energy of the orders. A brushless motor that generates relatively high frequency orders with relatively less energy would therefore be desirable because such orders will be masked by the noise of the blower and advantageously be inaudible.